1. Field of the Invention
In an automatic transmission for a vehicle having a plurality of friction engaging elements (hereinafter “engaging elements”) and a one-way clutch, the invention relates to automatic transmission controlling apparatus and method that reduces gear shifting shock when a gear shift is performed that engages the one-way clutch from the disengaged condition.
2. Description of the Related Art
A known automatic transmission has a one-way clutch and engaging elements that allow transmission of torque in one rotational direction but does not transmit torque in the reverse direction. In the automatic transmission described in the Japanese Patent Application Publication No. 11-159603 (JP-A-11-159603), for example, when a gear shift is performed in which the engaging element is disengaged and also the one-way clutch is engaged from the disengaged condition, when the one-way clutch goes into the engaged condition, gear shifting shock occurs.
In order to reduce the gear shifting shock, the JP-A-11-159603 discloses an automatic transmission that, when a gear shift is performed in the direction in which a disengaged-side engaging element is disengaged from the engaged condition and a one-way clutch is engaged from the disengaged condition, makes the speed of deforming of the disengaged-side engaging element small. The Japanese Patent Application Publication No. 10-68334 (JP-A-10-68334) discloses an automatic transmission that, when a downshift is executed, controls the ignition timing of an engine toward the retard angle side to reduce the engine torque and, by extension, reduces the input torque to the automatic transmission, thereby softening the gear shifting shock occurring when the one-way clutch is synchronized.
It is difficult, however, for the art noted in the JP-A-11-159603 to control the rate of change of the rotational speed of the input side of the clutch, and gear shifting shock still occurs when the one-way clutch engages. Also, the automatic transmission according to the art of the JP-A-10-68334 cannot soften the gear shifting shock in the case in which the engine cooling water temperature is low and retard angle control is prohibited. Even if the engine torque is made zero, because of the influence of reaction force to the decelerating of the vehicle a gear shifting shock occurs when the one-way clutch is synchronized. Additionally, when the engine ignition timing is in retard angle control, if the ignition timing of the engine is excessively retarded, there is a possibility that the engine will stall, and for that reason the degree of freedom of control is reduced.